The aim of this program is to increase the basic understanding of how innate behavior patterns (i.e. "fixed action patterns") and recognition mechanisms (i.e. "innate releasing mechanisms") are coded in and controlled by the nervous system. For this purpose, anuran (toads and frogs) acoustic behavior, i.e. calling and responses to calls, is being studied. This behavior is especially appropriate because of its relative simplicity, the species-specificity of some calls, and the fact that some calls can be elicited in essentially normal form by brain stimulation. Anurans are especially appropriate because of their high tolerance of radical surgical procedures, accessibility and simplicity of their nervous systems, and ready availability and maintenance. The main method to be used is an isolated brainstem preparation. In this technique, the brainstem of a male leopard frog is removed and placed in a tissue bath. The mating calling circuits are then activated by electrical stimulation of the preoptic area and neural correlates of calling are recorded from the laryngeal nerves and from the brainstem. This technique will be used in electrophysiological, lesioning, and neurohistological studies of the calling circuits of adult frogs and in studies of the development of the calling circuits.